The plate heat exchanger is superimposed by a certain shape corrugated sheet and a phe gasket, and assembled by frame clamping. The cold and hot fluids respectively flow through the flow channels on both sides of the corrugated plate, and exchange heat through the plates. The corrugated board is usually made of a thin plate of stainless steel, aluminum, titanium, molybdenum or the like having a thickness of 0.5 to 3 mm. The advantage of the flat heat exchanger is that the heat transfer coefficient is high (about 2 to 4 times higher than that of the shell-and-tube heat exchanger), it is easy to remove and wash, and the number of plates can be increased or decreased to adjust the heat transfer area. The disadvantages of flat heat exchangers are mainly due to the limitations of structural strength and gasket material, low operating pressures and temperatures, and limited processing capacity due to the small gap between the plates. Generally, the operating pressure should be controlled below 1.5 MPa; for synthetic rubber gaskets, the applicable temperature should not be higher than 130 ° C, and for compressed asbestos gaskets, the applicable temperature should not be higher than 250 ° C.